Why is Darnay ccontinuing with the "Patsy Did It" mantra?

That is a very good question. What is the reason? It cannot be something as simple as the "sore loser" syndrome, could it? Or, trying to revive a very tarnished reputation? This dirt just tarnishes it more, don't you think? This email of the book chapter is in extremely poor taste. Darnay has revealed himself to be a poor strategizer throughout his involvement in this case. Is this just another example?